Method of processing electrical elements



p 1952 N. M. BROWN, 4R ETAL METHOD OF PROCESSING ELECTRICAL ELEMENTS Filed Sept. 10, 1949 AAiWAAA I .IIIV' "V smvnuomsrsrz I00 coo mpoo ,aoo

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wire 2- WOZEWENN- 4N V EN TORS o 50 mo I50 TEMPERRTURE m DEGREES CENTIGIZFIDE Patented Sept. 9, 1952 Norman M1r Brawl-i, Jr., Los kng'elgaiid primate A; Shank; Redondo Beach;"Callii!.;-fisifi6rt6 The Garrett- Cofporation;LosAngeles; Calif, at eornsirai q 0 Ga i lim ii etio gseiitemte 10, i949, 'seriai No. ii4936 1 your iii-Vfitioii relates in general to "eletrie al ae'mnts em 5, method or preeessingthe same,- emi peitiouiariy relates to a methoo of 'subjectirig a1 finishedorsempfimshed element to e; oel-ibraz tion procedure. I

F01 onvnieiice Gidesoriptim themethod will be described asit is applied- 12GSthe'cailibration ofelectrical resistors of the type known as glassbeadthermistor's,although we perceive our-invention itsbroaderiaspects' asb'eiixgnreadily adapte able to the processing of .other kinds of elec'str'ieal elements'1:epacitors, .for example.

Inthmanufature lofthesethermi'stors it ap; pears to be inherent that :elose teleranee values arenot readily obtainable. T111182,- thermistor supposedly having a,- nomina-l'value of 2,000 ohms at 25 'C.-,- may actuallyhave a. value anywhere between 166092400 ohms. That is,- it is manufece tured toe,- toleranceof plus or minus20%-, and it appears that closer tolerancevarlnes are not easily obtainable in present manufacturing processes without prohibitive cost. On the other hand, many circuit designsfor the use of such elements may have calibration tolerance requirements of theorder of plus or'minus 1%,- Pa rtieularly is this so in manyelectronie applications.-

Another objection to wide tolerances of eleei triea} elements isthe problem ofinte-mhan eability in critical'oircui-ts; That isto say, after an e ri a p r u ha be l ra e 1b he ct l e er i ent i s; Pa t cu a e e able from the standpoint of mainteneneeand ser-Vicing thetreplacemei t elem-entsin the eppz't; ratus not upset the ceiibration of the eircuitand resiglt miinsatis actory function after b ing Serveiced.

It is therefore a primary object of ouririvjen tion to provide a simple, inexpensive method of process ng electrical l eriieiits'to a desired clib'iaf tion tolerlii'ce. it further otject 150- Wa ne .2: iiiethofd of processing eiectri'ail elements or the t pe wherein a plurality" of con motors are intimately asset bitted with a separating medium, the sen me ium having ajprimary eie'triee enereeteristiewnicn it is'desiied to change so tiiattrie element when ealibrated'has" e; final electrical response char, acteris'tic' cilrife' that'is ufiohinged in shape; or slope but whidh ciirve' is confine within a desired cefibr tion' i e an e o "It is e partieularotjeetjto-pro;" of'pr'ocessifig thermistors or the b f .=,e e probe type, so that the thermistor. has I fingil elec: ri r nqfi c ere' fie ci r ps f'nn hen e snap'e or slope whih ve doni'lnedivithin a desired calitretiori tolerarie. Siierr ti-ierriiistois 1 simmer ((21. 51 281;)

:2 iisu'eiiy' cer' ipriseepeir eff eon-(motors imbedded in er eietrieezii-y essoeiated" with a e'edeifi iiietelli oxid semi-conductor, the whale tfifi being enelosed iri a; thin-grassenv eiope in intimate marin r eon'tat' therewith. p

It; is erurtnerobjem to p'ovide e; methodot roeessmg glass bead ther ms aiiid the rare wherepy tne resperise characteristic eurvesof tr eimistors ere'fiot altered with-respeet to shape er slope,- bet are i-nierei iiispiaced s'u stintiefl? linearly with respeet to 61 16 or me eeordinetes or theeurve;

Farther (sweets will be e peierittupon :ecirisi'e eration of the preferred embod-iment"tfietin verition shown on the drawing: and describe in detail l ieri-iiri. aforementioned, itzis' confirmepieteci the invention is adaptable use the calibration of other electrical :element'sTtl-iaifi thermistor-S, hence itis intended thatthe deserip' tive matter contained hereinlshalltbe interpreted as being exemplaryratherithaini as .liein-g izestrie tive oflthe scopie'iof the:ihveiitionl- Referring :tothe drawing, Fig; agreetly enlarged ross-sentinel view of atgl ass 'bead thermistor.-

Fig. 2 is a crossesectionalyie w ofaa gless-e 98d thermistorr'afterprocessing. Fig; 3 shows one methodoi prQfi6SS-ing-&bh91 mistor, together with the electrical eireuit used for cOntinuouscalibration; and: f g V fig. 4 shows charaeteris iec-urves pf thetheie misterbefore andxafter calibration.- In Fig,- 1 a b edr onv-e asswrebe' t pe'efithee: miste 191. s ow u atherm e er 1. ii es age es nrebez W hin whic er mhed ede heir .of-- =Q d e Q s 1? he nds i'WlL em ed ed n he beedxl? qemw il ed o a m ie ie x ii sem mm??? e hi glass en lee' 4 le nd Q heereb H= eeelese thegee e d wieue s z ,i r ub ee ie d s ie their length, ihb ewiermi New P b struct re haying requisite strength ridlrig i dity in thepraetige-of-"the inyention-afwhez'i bridge oiroliit lfl qr Fig;- :2 is "employed calibration vproeessing' of the therm Mathed resistors .21 endfi constitute he or thejbridge while a, nefer'enciii 23 and the thermistor to constitute the arms" or the bridge, 'E r-thehufiibs 'drina il tainifig'the reference thermistor {Kate eons figj'rlt -is well known manner through a series variable resistor 28 which is shunted by a normally-open switch 29. A switch 30 is provided to short-circuit the thermistor It for a purpose to be described below.

In the practice of our invention, we prefer that, for reference thermistor 23, one be selected possessing at any reference temperature the resistance at that temperature desired in the thermistor to be calibrated. That is, if it is desired to process thermistor to a nominal resistance of 1500 ohms at 100 F. within a tolerance of plus or minus 1 then it is preferable that thermistor 23 have the value of 1500 ohms at the temperature of 100 F. It is, of course, possible to correct for minor deviation therefrom by changing the values of matched resistors 2| and 22 in a manner known to those skilled in the art.

As noted hereinabove, the calibration process comprises, in general, changing the primary elecaccomplished in a variety of ways. For example,

it may be more expedient to remove portions by drilling, or by other methods dictated by choice or circumstances.

During the grinding process the temperature of thermistor 10 will be elevated, and it is possible for its temperature to rise to such an extent, above 575 F., for example, as to permanently change the temperature-response versus resistance characteristic of the element. In order to assure against such abnormal temperature rise, our invention contemplates the use of the bridge circuit in such manner that the galvanometer will give a partial scale reading during the grinding operation, before such limiting temperature is reached, for example, at 300 F.

The preliminary bridge calibration procedure for accomplishing such use of the bridge circuit isa's follows: (1) the reference thermistor 23, connected as shown, is placed in the bath 2d, which is conveniently at room temperature; (2) switch 29 remains open and switches 26 and 36 are closed; (3) variable resistor 28 is adjusted so that the galvanometer 27 gives a full scalereading; (4) thermistor i is replaced in the bridge by-a precision resistor having a resistance which is equal to that of a standard calibrated thermistor at 300 F.; (5) with switches 29 and open and switch 26 closed, the reading of galvanometer 2'! is noted; (6) the precision resistor is then replaced by thermistor l0.

4 Calibration processing of the thermistor [0 while it is in the circuit may now proceed by the grinding-operation aforementioned, taking care to observe the galvanometer during the operation, and whenever the temperature of the thermistor reaches 300 F. the galvanometer 2? will give a reading like that obtained in steps (4;) and (5) described above, at which time the grinding is stopped until the thermistor cools down;

Frequent checks of the progress are accom-- .plished by dipping the thermistor 10 into the uniform temperature bath24 and noting the galstanometer reading. As the reading approaches I the thermistor being processed.

zero the thermistor is approaching its specified calibration point. The switch 29 provides sensitivity of calibration without endangering the galvanometer by large bridge unbalances. Thus, as the galvanometer reading approaches zero when readings are taken, the switch 29 may be closed to provide more sensitive determination of the balance of thermistors l0 and 23. Switch 28 may be of the spring push button type in order that it will not be inadvertently left closed, and will be closed only when a sensitive reading is to be taken.

The scale of the galvanometer 27 may be graduated in percentages so as to give a direct reading of the percentage difference of resistance existing between the standard reference thermistor and In Way thermistors may be processed to any tolerance without changing any of the steps in the process.

It should be noted that it may be necessary to dip the thermistor it in a light machineoil or other suitable, protective coating medium (which maybe floated on the surface of the uniform temperature bath) prior to dipping it in the bath for calibration check. This is so if the bath is mercury or, other liquid conductive of electricity, otherwise the conductive liquid would short across the exposed surface of the bead l3 and conductors 2 to give ialse readings. With respect to the uniform, temperature bath, 24, we wish to point out that it need be at no particular temperature, since it merely insures that the immersed thermistors i0 and 23 are at the same temperature when readings are taken.

After the calibration processing is completed the end of the thermistor which has been exposed by grinding may be given a protective coating of varnish or other suitable material. A completed element, together with its protective coating 40 may appear like that shown in crosssecticn in Fig. 2.

Fig. 4 shows typical exemplary characteristic curves of a thermistor before and after calibration processing. It will be noted that the curve for the calibrated thermistor is displaced substantially linearly from the uncalibrated curve. This is accomplished by changing the primary electrical value of the separating medium without changing the inherent electrical response characteristics of the element. That is to say, in the case of a thermistor it is accomplished by changing the resistance of the bead i3 withbut changing the shape and slope of the characteristic curve by not permitting the processing temperature of the bead to rise above its critical Value. 7

' We claim:

1. A method for the calibration processing of a first electrical element to electrical equality with a standard reference second electrical element, said first element having a critical upper temperature, said method comprising: connecting said first and second elements in an electrical circuit comparison means having indication means so arranged as to give a first indication when said first element approaches its critical temperature during the processing and to give a second indicationwhen the processing is complete; and changing the mass of said first element without exceeding said first indicationby said indication means until said second indication is given.

2. The invention of claim 1 further characterized in that said processing results in a reduction of the mass of said first element.' v

3. A method for the calibration processing of a first electrical element to electrical equality with a standard reference second electrical element, said first element having a critical upper temperature, said processing to be completed at a reference temperature, said method comprising: connecting said first and second elements in an electrical circuit comparison means having with indication means so arranged as to give a first indication when said first element approaches its critical temperature during the processing and to give a second indication when the processing is complete; changing the mass of said first element without exceeding said first indication by said indication means; electrically comparing said first and second elements at said reference temperature; continuing to change the mass of said first element without exceeding said first indication by said indication means; and electrically comparing said first and second elements at said reference temperature until said second indication by said indication means is given at said reference temperature.

4. A method for the calibration processing of an electrical element having a critical upper temperature, said processing being done while said element is connected in electric circuit means having an indicating means arranged to give a first predetermined indication when said electrical element reaches its critical upper temperature during the processing, and to give a second predetermined indication when the calibration process is completed, said method comprising: changing the mass of said electrical element in such manner that said first predetermined indication is not exceeded, and continuing to change the mass until said second predetermined indication is shown. 7

5. The invention of claim 4 further characterized in that said processing results in reduction of the mass of said electrical element.

6. A method for the calibration processing of a first electrical element to a standard electrical reference at a reference temperature determined by a second electrical element, said first element having a critical upper temperature, said processing being done while both of said elements are connected in electric circuit means having an indicating means arranged to give a first predetermined indication when said first electrical element reaches its critical upper temperature during the processing, and to give a second predetermined indication when the process is completed, said method comprising: changing the mass of said first electrical element in such manner that said first predetermined indication is not exceeded; comparing electrically said first element with said second element at said reference temperature; and continuing to change the mass of said first element without exceeding said first predetermined indication until said second predetermined indication is shown at said reference temperature.

7. The invention of claim 6 further characterized in that said processing results in reduction of the mass of said first element.

NORMAN M. BROWN, JR. CLIFFORD A. SHANK.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,635,184 Jones July 12, 1927 1,962,438 Flanzer et al June 12, 1934 2,427,064 Moul Sept. 9, 1947 2,500,605 DeLange et a1 Mar. 14, 1950 

